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At present, the production of micro parts and components with characteristic sizes ranging from micron to millimeter mainly relies on micro machining technology, but the dimensional size of micro tools (including micro cutting tools, micro grinding tools, and microelectrodes) involved in micro machining is ultra small and made of super hard material like cemented carbide and polycrystalline diamond, which makes the preparation of ultra small micro tools have become the main bottleneck restricting the development of micro machining technology. The non-contact nature of electrical discharge machining (EDM) process makes it more competent in fabricating micro tools with relatively high efficiency and low cost; especially the wire electrical discharge grinding (WEDG) invented in 1985 provides a new approach and direction to fabricate micro tools; following this trend, numerous new design requirements and theoretical concepts of EDM-based processes utilized in fabricating micro tools have been proposed and studied successively, but, very few studies have been proceed from an integrated perspective. To address the gap, this study provides a comprehensive and well-arranged literature survey of the advancements made in the fabrication of micro tools using various EDM-based methods to date along with an insightful discussion on the science and application of EDM process. The critical factors influencing process performance, different numerical models, limitations, as well as possible future research direction and development in the field of micro tools fabricated by various EDM-based methods are identified and reviewed. This article is expected to help the researchers in identifying the existing gaps and contributing towards making EDM-based processes more competent in catering the trend of parameterized and non-standardized fabrication of ultra small micro tools. [ABSTRACT FROM AUTHOR]

The effect of solution heat treatment on the mechanical and microstructural properties of 316L stainless steel parts fabricated through hybrid additive and subtractive process (HASP) is explored. These techniques synergistically combine additive manufacturing directed energy deposition (DED) with subtractive manufacturing (SM) technique in a single machine, and they provide an important opportunity to improve material utilization, part complexity and quality management in functional components. Thin-wall specimens were manufactured by HASP to investigate the effect of the solution heat treatment at different temperatures and different holding times on the microstructure and the resultant mechanical properties, such as the Vickers micro-hardness and tensile property. The results show that the content of δ and σ phases can be optimized via heat treatment. While the solution treatment temperature and time increase, the content of the σ and δ phases in the γ matrix can distinctly decrease, which causes the strength to degrade but the ductility to increase. These results suggest that the microstructure and the resulting mechanical properties of HASP-fabricated samples can be adjusted through the adjustment of solution heat treatment. [ABSTRACT FROM AUTHOR]

This paper proposes a strategy to overcome the problem of poor surface quality when grinding difficult-to-cut materials at a small scale, by creating a small-scale grinding tool with a regular array structure (SSGT-RAS) through the method of combining low-speed wire electrical discharge turning (LS-WEDT) machine technology and electroplating process. A numerical model is established to describe the surface topography of SSGT-RAS grinding of titanium alloy Ti-6Al-4V, taking into account the shape, size and distribution of the abrasive grains, the plastic material removal mechanism and the machining parameters. The study comparatively analyses the surface morphology characteristics and surface generation mechanism of SSGT-RAS and ordinary cylindrical grinding tool (OCGT) when grinding titanium alloy Ti-6Al-4V with different helical groove depths through side dry grinding experiments. The experimental results show that SSGT-RAS improves the surface quality of the workpiece compared to OCGT, and surface roughness Ra can be reduced by up to 25.20 ~ 27.81% and 21.49 ~ 35.44% at most by changing the feeding velocity and cutting depth, respectively. In addition, increasing helical groove depth further improves the surface quality. A comparative analysis of the simulation and experimental results shows that the prediction error of the surface roughness Ra is within 15.92%. This research expands the preparation process of surface-structured grinding tool at small scale, which has significant theoretical and engineering applications. [ABSTRACT FROM AUTHOR]

This research explores the intricate dynamics of machining nickel-based single crystal superalloys, with a focused examination of the principal parameters influencing grinding forces and surface roughness. It marries micro-scale grinding simulations with sophisticated Support Vector Machine (SVM) modeling in Matlab, conducting an in-depth analysis of how variables such as grinding depth, abrasive grain size, spindle speed, and feed rate affect the surface integrity of these premium materials. The introduction of the SVM model represents a novel contribution to the field, undergoing extensive validation against traditional predictive methods and demonstrating superior predictive accuracy. Detailed investigation into grinding parameters uncovers a significant link between process variables and the microstructural alterations on the alloy's surface, leading to the determination of grinding conditions that substantially enhance surface quality. The accuracy of the SVM model in predicting surface roughness, evidenced by a Mean Squared Error (MSE) of 9.9662e-05 and an R-squared value of 99.9992%, positions it as a pivotal tool for process optimization. This, in turn, offers substantial advantages for precision engineering in aerospace component manufacturing. The findings underscore the transformative impact of SVM-based modeling in realizing exceptional performance in the machining of complex materials. [ABSTRACT FROM AUTHOR]

Nickel-based single-crystal superalloys are widely used in aerospace and industrial gas turbine blades due to their excellent material properties. However, these alloys are also known for their difficulty in machining due to their superior physical properties. To improve the surface quality of machined parts, this study investigates the effects of different grinding conditions (dry grinding, flood, minimum quantity lubrication (MQL)) on the surface morphology, grinding-induced damage layer, and subsurface microstructure of nickel-based single-crystal superalloys. The experiments show that under MQL conditions, as the wheel speed increases, the grinding marks become more uniform, surface micro-defects decrease, and surface quality improves. A comparison of the thickness of the grinding-induced damage layer (D) obtained from dry grinding, flood, and MQL reveals that MQL cooling is more effective in reducing the damage layer thickness of nickel-based single-crystal superalloys compared to flood cooling. With an increase in wheel speed from 15 to 35 m/s, the thickness of the subsurface damage layer reduced from 14.2 to 11.4 µm using emulsion cooling and from 12.8 to 9.1 µm using MQL cooling. Unlike dry grinding, the use of grinding fluid significantly impacts the subsurface microstructure of the alloy, effectively suppressing work hardening and reducing the thickness of the grinding-induced damage layer, thereby improving the surface quality. It has important theoretical and practical significance to improve the quality of grinding surface. [ABSTRACT FROM AUTHOR]

The microstructure, hardness, and fracture strength of Inconel 718 fabricated with laser metal deposition are investigated. The solution treatment plus aging (STA) (including 980 °C, 720 °C, and 620 °C for 1, 8, and 8 h, respectively) and low-temperature stress-relief annealing (LTSLA) (including 650 °C for 1 h) are compared, which can respectively improve the hardness and tensile properties. Results show that the as-deposited sample mainly contained γ matrix, coarse Laves phase, granular carbides, and nitrides. STA and LTSLA post-heat treatments could respectively improve the hardness and tensile properties, while the elongation slightly decreased. The solution treatment promoted almost Laves phase to dissolve into γ matrix and homogenized the matrix, and the aging treatment promoted the precipitation of γ′ and γ″ phases, which significantly improved the mechanical properties. [ABSTRACT FROM AUTHOR]

The uncontrollable directional grain growth and non-equilibrium microstructure of Inconel 718 will form during laser direct energy deposition (LDED), which seriously limits the promotion and application, so it is necessary to consider the heat treatment to improve the microstructure and mechanical properties. In this paper, the effects adopting different heat treatments on the phase composition, precipitation behavior, grain structure, tensile and tribological properties of LDED Inconel 718 have been systematically investigated, with as-deposited samples compared. The results show that the number and size of γ″ phases can be significantly changed under different aging and solution conditions, and the strength and wear resistance increase while elongation decreases since the fine grain and precipitation strengthening occurring during heat treatment. By comparing the different samples, the SA1100A exhibits the highest yield and tensile strength, with 140.6% of yield strength and 83.9% of ultimate tensile strength increasing compared to as-deposited samples, also showing the narrowest wear mark width and the lowest average mass loss. [ABSTRACT FROM AUTHOR]

• Thin wall parts of GH4169 and GH3536 superalloys were prepared by direct energy deposition. • The properties of the two superalloys before and after solution aging heat treatment were compared. • It provides some data support for the preparation of GH4169 and GH3536 functionally graded materials. In this study, thin-walled parts of GH4169 and GH3536 superalloys were prepared using the direct energy deposition (DED) method, respectively. The results revealed that solution aging treatment was effective in eliminating the boundary of the molten pool and refining the grain structure to some extent. Subsequently, the Laves phase redissolved in the γ matrix, releasing Nb element. This was followed by the formation of γ′, γ″, and δ phases, which effectively improved the yield strength and tensile strength of the GH4169 alloy after high temperature heat treatment. In the case of the GH3536 alloy, heat treatment caused a change in microstructure from columnar crystals to larger equiaxed crystals. Additionally, chain carbides precipitated at the grain boundaries, which increased the elongation after fracture but decreased the yield strength and tensile strength to some extent. Following solid solution aging treatment, the ultimate tensile strength of GH4169 deposited parts exhibited a 27.7% increase in the deposition direction and a 15.6% increase in the laser scanning direction. Conversely, the tensile strength of GH3536 showed minimal variations, but the elongation in both directions experienced notable improvements, rising by 22% and 20.7%, respectively. Solution aging treatment further eliminated the mechanical anisotropy of the two superalloys due to the inhomogeneity of microstructure and grains, as well as the existence of molten pool boundaries and grain boundary segregation. Furthermore, the microstructure and mechanical properties of GH3536 alloy were found to be better than those of GH4169 alloy, both before and after aging. [ABSTRACT FROM AUTHOR]

The microstructural characteristics and mechanical properties of forged parts differ significantly from those of additively manufactured parts, which results in different machinability. In this paper, the microstructure effect on the machinability of Inconel 718 parts obtained by different manufacturing processes, laser directed energy deposition (LDED), laser powder bed fusion (LPBF) and forging, is evaluated and critically discussed in terms of milling forces, surface morphology, surface roughness, chip morphology and subsurface microstructure. The results show that due to having the smallest grain size, high dislocation density, and precipitation hardening provided by the reinforcing phases, the milling force is maximized when cutting LPBF Inconel 718 parts. In addition to grain size and dislocation density, the texture also has an effect on the plastic deformation of the subsurface after milling. Furthermore, LDED and forged Inconel 718 parts undergo a continuous dynamic recrystallization process characterized by sub-grain rotation transforming low angle grain boundaries into high angle grain boundaries during milling. This study provides some theoretical guidance for the integration of additive and subtractive processes in the machining of complex structural parts with Inconel 718 alloy. [ABSTRACT FROM AUTHOR]

The present work investigates the influence of the laser power (P) and scanning speed (v) on the surface morphology and Vickers microhardness of single scan tracks formed by directed energy deposition (DED) to determine suitable parameter values for further in-depth investigation of additive and subtractive hybrid manufacturing (ASHM) of fabricated parts. The experimental results show that the depth and width of the melt pool depended significantly on both P and v. Furthermore, the anisotropic mechanical behavior of bulk 316L specimens fabricated by ASHM in the horizontal (H), edge (E), and vertical (V) directions relating to the build layers was also explored. The results show that the tensile strength of the specimens fabricated by ASHM in the H direction was higher than that of those built in the E or V direction, implying that the anisotropy originates from the unique thermal history of each component location owing to the layer-by-layer nature of the DED process. [ABSTRACT FROM AUTHOR]

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A quasi-analytical solution on the minimum length and its corresponding system energy is proposed for the stable multi-layer folded graphene wrinkles (FGWs). The quasi-analytical solution shows that: (1) at a certain threshold height, a single-layer FGW becomes energetically favorable compared to a standing graphene wrinkle. (2) All the geometrical properties of single-layer FGW reproduce in the double-layer FGWs, which is considered as the typical configuration for predicting the multi-layer folded FGWs. (3) Parametric studies show that the increased bending stiffness per length promotes the minimum graphene length while the case is reversed for the increased adhesion energy density. Both of the increased bending stiffness per length and adhesion energy density lead to the decreased system energy for the stable folded structure, while the system energy is less sensitive to the variation of adhesion energy density compared to that of the bending stiffness per length. Besides, molecular mechanics simulation shows that the present model has high accuracy on evaluating the system energy and the configuration for multi-layer FGWs. [ABSTRACT FROM AUTHOR]

In order to improve the micro-grinding quality of 2.5D carbon fiber-reinforced silicon carbide ceramic matrix (2.5D Cf/SiC) composite materials, their characteristics under different grinding parameters were investigated in this study. Firstly, theoretical models for the undeformed chip thickness and micro-grinding force were established. Then, orthogonal and single-factor experiments were conducted using 0.9-mm-diameter micro-grinding tools electroplated with 500# diamond abrasive particles. Through the range and variance analysis of the orthogonal experimental results, the order in which grinding parameters affect the grinding performance of 2.5D Cf/SiC composites was obtained. Single-factor experimental results indicate that the theoretical model of the micro-grinding force shows consistent trends with the experimental results. As the grinding depth ap and the feed speed vw increase, the grinding force, the surface roughness Ra, and surface defects after micro-grinding also increase, indicating that the grinding performance of 2.5D Cf/SiC composites gradually deteriorates. On the contrary, increasing the grinding speed vs can improve their grinding performance. Based on the established theoretical model, the reasons for the variation of grinding force, surface morphology, and surface roughness with grinding parameters were elaborated. This research would supply a basis for understanding the micro-grinding performance and provide guidance for improving the micro-grinding quality of 2.5D Cf/SiC composites. [ABSTRACT FROM AUTHOR]

Nickel-based single crystal superalloys have broad application prospects in the aerospace field. Their excellent physical properties enable the workpiece to serve in complex environments for a long time, and are often used in the most complex stress and the worst working conditions. However, the damage caused by mechanical material removal deteriorates the wafer surface flatness and die strength, while its surface and subsurface formation principle has yet to be revealed. This study aims to analyze the influence of abrasive particles on the load of the workpiece during machining was scrutinized through the lens of stress tensor, yield performance, and third invariant. The results indicate that, a substantial stress load is exerted on the front end of the abrasive grain, leading to the yield deformation of the workpiece. Conversely, the stress load at the bottom of the abrasive grain is comparatively lower, resulting in tensile deformation and the formation of a discernible plastic damage layer. To delve deeper into the workpiece's damage phenomenon, this study conducts a comparative analysis from the standpoints of chips, surface morphology, and subsurface characteristics of DD5. Experimental results indicate that the chips on the contact surface exhibits a relatively smooth texture, while the grinding surface manifests grooves of varying depths. Concurrently, subsurface analysis reveals the presence of slip deformation and elemental flow. This investigation elucidates the intricate interplay between the grinding process and subsurface loading, offering valuable insights to enhance the quality and precision of nickel-based single-crystal superalloy workpiece manufacturing. • The stress load is impacted by the variation in grinding parameters, but the stress value applied by abrasive is slightly affected. • Subsurface deformation is linked to the frequency of serrated chip formation. • Low wheel speed combined with high feed rate and grinding depth causes more noticeable scratches on the workpiece's surface. • Workpiece surface becomes more microhard than the substrate, and the microhardness is increased by about 15 μm. [ABSTRACT FROM AUTHOR]

• Microstructure and mechanical properties of Inconel 718 parts prepared by LDED and SLM have been systematically investigated and compared with the conventional forged-parts. • The microstructure evolution is influenced by the crystal preferred orientation and the temperature gradient. • The difference in crystallographic texture between SLM and LDED-parts result in the different mechanical property anisotropy. This paper systematically investigates the microstructure, crystal structure and related mechanical properties of Inconel 718 thin walls prepared by two different methods, laser direct energy deposition (LDED) and selective laser melting (SLM), which are representative technologies for laser additive manufacturing of high-performance metal parts, and compares with conventional forged parts. The microstructure of SLM-part consists of columnar and equiaxed crystals with disordered growth directions, while LDED-part is mainly composed of coarse columnar crystals that grow perpendicular to the plane of the molten pool free surface. Unlike a strong 〈001〉 texture in the LDED-part, the SLM-part has a {110} texture in the XY plane, achieving stronger tensile strength due to different grain boundary strengthening and dislocation strengthening effects, which is found by comparing with LDED and forged Inconel 718 alloy. In addition, the difference in crystallographic texture between SLM and LDED-parts results in the different mechanical property anisotropy. The comparative study of two laser additive manufacturing technologies provides guidance for an in-depth understanding about the mechanism of laser additive manufacturing high-performance metal parts. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behavior during grinding and static recrystallization (SRX) behavior during thermal exposure of Ni-based single crystal alloy were compared in this work. The microstructure changes after DRX and SRX were characterized by field emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM). The grain orientation and dislocation density distribution were analyzed by transmission Kikuchi diffraction (TKD) and electron backscatter diffraction (EBSD). The results show that SRX is affected by DRX process on the ground subsurface of single crystal alloy. The nucleation sites of SRX at high temperature are derived from significant number of high-density dislocation structures generated by DRX that induced by grinding process. Compared with the equiaxed nanograins produced by DRX, micron-scale cellular and equiaxed grains are formed on the surface, and dislocation density decreases sharply after SRX. The original cube texture of single crystal superalloy changes into shear texture due to plastic deformation during grinding, and then into strong recrystallization texture at high temperature. The microstructure changes under deformation and high temperature directly affect the final properties of single crystal blades. It is of great practical significance to understand the microstructure evolution and grain orientation changes during DRX and SRX processes, so as to reveal the mechanism of single crystal transforming into polycrystal from machining process to service stage of single crystal blades. • The relationship between dynamic recrystallization and static recrystallization of single crystal alloy is established. • The microstructure evolution of machined surface from single crystal to polycrystalline is revealed. • The orientation and texture changes of the recrystallized grains were obtained. [ABSTRACT FROM AUTHOR]

• The feature – Edge, which can represent the whole point cloud is introduced into the iterative calculation to reduce the mismatch between corresponding points and improve the convergence speed. • The variance minimization objective function based on bi-direction of normal and tangential distance is used to make the allowance distribution uniform while reducing the tangential runout of the point cloud. • In order to make up for missing points when extracting the edge of point cloud, the extracted edge points are converted into curvature space. Curvature octree is used to search for points with similar curvature degrees, so that the set of points sufficient to represent the global point cloud can participate in the subsequent calculation. The basis for guidance in the field of automated robot processing is modeling by visual scanning. Matching algorithms are the real link that can be made between the ideal model and the subsequent robot processing. The matching algorithm that meets the machining requirements plays a pivotal role in the entire process, which provides the exact location of design models and measurement data. In order to meet the requirement of making the machining allowance uniform, a fine registration method which considers the variance minimization of the normal and tangential distances between the edge neighbors of the scattered point cloud is proposed. The edge neighbors are achieved by local growing of edge seeds based on the minimization of energy of supervoxel, which can represent the model more accurate than edge points extracted directly. The edge neighbor points are used to participate in the calculation, and the objective function of minimizing the variance of the two-way distance with the introduction of weight coefficients is proposed to constrain the iterative process. The effect of the distance in two directions on the result is analyzed, to determine the appropriate weight coefficients so that the matching calculation converges quickly and accurately. In comparison with other classical and state-of-the-art matching methods, the method in this paper performs well in terms of solution efficiency and accuracy of results. Moreover, the ability of this paper's method to resist Gaussian noise is investigated, and it is found that this paper's method has good robustness when σ is less than 1 for Gaussian noise. Ultimately, a uniformly distributed residual model is obtained to provide a visually guided basis for subsequent machining. [ABSTRACT FROM AUTHOR]

As a critically issue in the maintaining of desired part quality and manufacturing productivity, tool condition monitoring (TCM) problem is treated by multi data-driven machine learning methods with training and testing datasets generated by stochastic segmentation. For existing methods, it is assumed that samples collected from same type tools follow identical probability distribution. Different from regular tools, abrasive tools dissatisfy this assumption because of their stochastic surface morphologies. Therefore, traditional data-driven methods loss their accuracies in abrasive tool changing cases. In data driven TCM models, the macroscopic effect of abrasive tool micro-stochasticity is discovered. For the abrasive tool frequently changing cases, an abrasive tool condition monitoring (ATCM) method based on unsupervised domain adaptation is presented to deal with changes caused by stochastic surface morphology. In feature-based transfer learning, source and target domain datasets are projected into a transferred subspace to enhance the distribution alignment similarity of two domains. A weighted maximum margin criterion (WMMC) is adopted in the domain adaptation process to make the transformed samples in same class closing but segregated from those in different classes. With unsupervised domain adaptation mechanism and multilayer perceptron (MLP), the unsupervised domain adaptation is proposed to deal with traditional model invalidation after abrasive tool changes. The proposed method is verified by the robotic belt grinding experiment results. Compared with the existing data-driven method, the weighted maximum margin criterion joint distribution adaptation (WMMC-JDA) based ATCM method still maintains the predicting effectiveness after abrasive tool changes. [ABSTRACT FROM AUTHOR]

This study delves into the grinding-induced microstructural and mechanical evolution in high-entropy nickel-based superalloys GH4169 and DD5, underscoring their distinct behaviors under varying machining conditions. Leveraging "Random Substitution" in Material Studio, the research developed intricate atomic models to accurately depict the complex chemical compositions and microstructures of these superalloys. Neper software was employed for multi-scale modeling, specifically analyzing the unit cells of GH4169. A critical focus was placed on the effects of key grinding parameters—depth, spindle speed, and feed rate—on the crystallographic deformation of GH4169, contrasting it with the response of DD5. The study highlighted a notable transition in GH4169's material removal mechanism from plastic flow to chip spallation at enhanced grinding depths and feed rates, while maintaining lattice integrity at higher grinding speeds. GH4169 consistently demonstrated greater tangential and normal forces during grinding compared to DD5, reflecting intricate machining complexities. The differential crystal orientations between these superalloys significantly impacted the grinding force distribution and heat dissipation during the process. This comprehensive analysis provides pivotal insights into the micro-level grinding process parameters, enriching both theoretical and practical understanding of material machinability in advanced manufacturing contexts. The study's novelty lies in its application of detailed atomic models and multi-scale modeling to uncover subtle microstructural and mechanical dynamics during the grinding of superalloys. [ABSTRACT FROM AUTHOR]

This study investigates the microstructure damage mechanism of the difficult-to-machine material nickel-base single crystal superalloy DD5 by analyzing the working condition load and crystal deformation. The complexity of the macroscopic and microscopic deformation phenomena during the machining process makes it challenging to study the damage mechanism of the workpiece. Hence, crystal kinematics equation is established using true stress-true strain theory, and the internal force balance and constitutive model of the crystal are analyzed. The proposed theory is applied to finite element processing and experimental analysis of the workpiece, and the subsurface deformation behavior is studied from a mechanistic perspective.The stress model is employed to explore the plastic flow phenomenon of the material during the machining process, and the influence of stress and shear force on the subsurface of the workpiece is discussed. The theoretical analysis of crystal deformation, based on the principles of materials science and mechanics, uncovers the relationship between subsurface deformation curvature and stress. The study delves into the effects of the grinding process on subsurface damage and deformation by analyzing the phenomena of plastic flow, plastic slip, and plastic winding in the subsurface microstructure. The results indicate that at grinding speed v s = 25 m/s and grinding depth a p = 60 μm, the damage to the subsurface deformation layer is minimal. The grinding process considerably impacts the stress exerted on the workpiece, with an amplitude ranging from 1.255 × 103 to 1.286 × 103. Conversely, the strain on the workpiece is relatively less affected by the grinding process, exhibiting an amplitude of 2.366–3.568. Moreover, when the normal stress and shear force of the abrasive particles form 45° angle, the subsurface deformation of DD5 manifests a distinct slip distortion at an approximate 45° curvature. • When the subsurface reaches internal stress balance f + div ∑ = 0 , the shear force is ν and the internal force is 1 − 2 ν. • With the development of technology, a grinding speed of v s = 25 m/s and grinding depth of a p = 60 μm can result in an effective removal of nickel-based superalloy DD5. • During grinding, the grinding depth is directly proportional to the true strain, whereas the grinding speed is inversely proportional to the true strain. • Subsurface crystal plastic slip and grinding direction mostly display 45° angle slip. [ABSTRACT FROM AUTHOR]